1. Technical Field
The present invention relates to a plasma etching apparatus, and more particularly, to a method of removing film materials on an edge area of a substrate in the plasma etching apparatus.
2. Description of the Related Art
Semiconductor devices and liquid crystal display devices are fabricated on substrates through multiple thin film deposition and etching processes. That is, a thin film is deposited on a substrate, and a portion of the thin film at the center of the substrate is removed through an etching process using an etching mask, thereby forming a device with a desired thin film pattern. However, since a thin film is formed over the entire surface of the substrate upon deposition of the thin film and an etching process targets on a portion of the thin film at the center of the substrate, portions of the thin film in an edge area of the substrate remain un-removed. In addition, during the etching process, particles or the like are likely accumulated in the edge area of the substrate. In a case where subsequent processes are carried out without removing the thin film or accumulated particles in the edge area of the substrate, many problems may occur, for example, the substrate may be distorted, or the alignment of the substrate may not be easily achieved.
Therefore, in order to perform etching for an edge area of a substrate, many attempts have been actively made to develop an apparatus in which only the edge area of the substrate are caused to be exposed and only the exposed edge area can be etched.
The thin film and the particles in the edge area of the substrate can be removed through a wet- or dry-etching process. In case of the wet-etching process, it is difficult to locally remove the thin film and the particles only in the edge area of the substrate due to difficulty in controlling the process. In addition, the use of various chemicals leads to an increase in production costs and causes environmental problems such as wastewater treatment.
On the other hand, in case of the dry-etching process, plasma is used to remove the thin film or the particles in the edge area of the substrate. This process has advantages in that the above problems with the wet-etching process can be solved.
Here, plasma refers to ionized gas that is composed of ions, electrons, radicals and the like. This plasma is generated at an ultra-high temperature, a strong electric field, or a high frequency electromagnetic field. In particular, the generation of plasma through glow discharging is achieved by free electrons excited under a direct current or a high-frequency electromagnetic field. The excited free electrons collide with gas molecules to produce an active group such as ions, radicals, and electrons. This active group physically and chemically affects the surface of a material, thereby changing the characteristics of the surface.
In an etching apparatus using such plasma, glow discharging occurs inside a container with a process gas therein to generate plasma that in turn is used to etch a work piece such as a substrate.
A conventional plasma etching apparatus for etching an edge area of a substrate using plasma is disclosed in Korean Patent Publication No. 10-0433008. In this patent, the diameter of a stage is made less than that of a wafer. The spacing between the stage and an insulator is established to be closer than the spacing between a cathode ring and an anode ring. The anode ring is installed at an outer periphery of the insulator. Concentrically installed on the outer periphery of the anode ring is a view ring that has an edge extending to be close to the cathode ring, such that the view ring can shield the surrounding of the stage except for a predetermined gap defined in-between with an outer peripheral surface of the cathode ring. An RF output terminal is connected to the cathode ring.
As described above, the cathode ring and the anode ring are installed at the stage with a diameter less than that of a wafer and the outer periphery of the insulator, respectively, and plasma is generated through discharging between the cathode ring and the anode ring. The view ring is installed around the cathode ring such that plasma can reach a bottom surface of an edge of the wafer, thereby performing plasma etching to the bottom surface of the edge of the wafer.
However, since a conventional plasma etching apparatus for etching an edge area of a substrate is a capacitive coupled plasma (CCP) type, wherein plasma is generated through discharging between two opposite electrodes, the apparatus has a disadvantage in that an etching rate is deteriorated due to lower density of plasma. In addition, since the electrodes are attached to the stage and the outer periphery of the insulator and plasma is generated under a high pressure, there is a problem in that in a case where the conventional apparatus is used to etch an edge area of the wafer, the plasma is spread to a central area of the wafer, so that a pattern at the central area thereof may be affected or damaged.
In addition, gases produced during the etching process cannot be smoothly exhausted from spaces defined by the cathode ring, the anode ring and the view ring. Thus, there is a problem in that particles generated during etching cannot be effectively removed and thus may be accumulated at a lower portion of the substrate.